Airwaves: August 5, 2011
Can You hear Me Now?
Theres been a lot of talk over the past few years regarding interference
on the AM and FM bands. Actually, the discussion goes back decades, to the
very start of experimental radio broadcasts -- one of the reasons Edwin Armstrong
invented FM is that he couldnt stand the interference he heard on his
(and others) first radio invention, AM -- but the topic has been getting more
traction ever since the FCC allowed digital HD Radio broadcasts.
HD Radio itself can cause problems, especially on the AM band where stations
are very close together compared with FM and television. This is due to the
digital broadcasts surpassing the bandwidth of regular music or talk programming,
and radios sometimes picking up the digital hash. On AM it is like
hearing white noise over weak stations, on FM it theoretically can cause FM
radios to become confused and make weak or distant stations simply
disappear.
But is HD Radio getting too much of the blame? As I said, interference has
been a problem since the beginning of radio. First it was natural -- lightening,
for example -- and eventually man-made. And it is definitely a problem, especially
when you consider that early 50-watt AM stations could be heard across the
country in the 1920s ... 50 watts would barely get you across the street today.
So whats the problem? LED traffic lights? Power lines? Neon signs? Yes,
to a point. All of those have the potential to hurt reception of both AM and
FM broadcasts. But it turns out that most reception problems are closer to
home. Your home, and what you have inside.
The cell phone charger you keep plugged in? Noisy interference unit. Your DVD
player? Same thing. Your cable box and big-screen television? You guessed it.
And while all of these items have been long known to cause problems directly
to AM stations, Steve Johnson, engineer for Wisconsin Public Radio found that
they cause problems for FM. Not just analog FM, by the way, HD FM is affected
too. SO HD isnt necessarily to blame for reception troubles, at least
when it comes to FM.
Johnson took measurements throughout homes in the Wisconsin area, sparked by
an increase of 37 percent of the number of listener complaints regarding decreased
reception of the stations he oversees. He found that interference indoors was
higher than outdoors, even if it was just outside the house. It didnt
matter if it was an urban apartment, an office, or a suburban house, the result
was the same: greatly increased interference -- as much as 20 to 30 dB -- and
lessened reception indoors.
He found that recently manufactured plug-in wall-wart power supplies,
as found powering small electronics, were the worst offenders. Some HD televisions
and DVD players were bad as well, something Johnson feels may also be power-supply
related. Computers, and in fact almost any electronic device, have the potential
to wreak havoc with radio reception on AM, FM and even television. Sometimes
it was a manufacturing problem -- shielding missing from a battery charger
built in China, other times it is the actual circuit design.
Long-term, Johnson says that broadcasters must insist that products do not
cause interference ... something that already is a requirement of the FCC but
is obviously not necessarily enforced. Short-term, you may have to move your
radio (often a few feet or a small turn will improve things noticeably) or
install an outdoor antenna if you are having problems picking up your favorite
station.
HD Update
Mexico has decided to allow the HD Radio system to be used by broadcasters
throughout the country; previously they had allowed such broadcasts by stations
within 200 miles of the United States border. It is not the digital
broadcast standard, however, so it is possible that another system could be
introduced in the future.
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Copyright © 2011 Richard Wagoner and Los Angeles Newspaper Group.
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